The present invention relates to an apparatus for classifying powdered bulk materials, particularly ground clinker, limestone or cement raw material, by air sifting, the material to be classified being fed via a material inlet in the cover plate of a cylindrical rotor with vertically extending rotor blades and charged into a sifting space having the shape of a cylindrical ring which extends between the rotor and a stationary vane ring surrounding and spaced from the rotor, through which ring sifting air is drawn-in approximately tangentially by a fan located on the outside so that the fine material contained in the material which is charged is conveyed into the inside of the rotor as a result of the suction action which results from the difference between the conveying action of the fan and the radially outward-directed conveying action of the rotor, conducted vertically downward through a pipe and fed to a subsequent separating device for the separating of fine material and sifting air, while the coarse material drops down in the sifting space and is discharged via a coarse-material discharge which is passed through by the fine-material/sifting air discharge pipe.
Apparatus of the above-described type for the classifying of powdered bulk materials by sifting air are well known. They have the advantage, it is true, of good sharpness of separation as a result of the sifting space of annular cylindrical shape, but in order to control different rates of flow of bulk material a plurality of such sifters of different size are required.
The object of the present invention is to improve the aforementioned known apparatus for purpose of equalization of the air distribution over the circumference of the apparatus by simplification of its construction so as, instead of a plurality of, as a whole--particularly in diameter--different structural sizes in order to cover the different rates of flow, to be able to use a single structural form with constant base parts of the same diameter.